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The actual distribution of residual oil requires that EOR
methods first of all effectively influence oil in flooded and gassy
areas as well as by-passed zones not covered by the current
system of oil production.
It is absolutely obvious that with such a wide variety of
the residual oil saturation conditions as well as under large
differences in the physical properties of oil, water, gas and
permeability of oil-saturated zones there cannot one universal
method for enhanced oil recovery.
All the known EOR methods are generally classified as
follows:
1. Thermal EOR
• Steam treatment;
• In situ combustion;
• Hot water flooding;
• Cyclic steam treatment.
2. Gas EOR
• Air injection;
• Light hydrocarbons injection;
• Carbon dioxide injection;
• Nitrogen, flue and other gases injection.
3. Chemical EOR
• Surfactant flooding (including foam);
• Polymer displacement;
• Alkaline displacement;
• Acid displacement;
• Chemical reagents displacement (including micellar-polymer
flood, etc.);
• Microbiological treatment.
4. Hydrodynamic EOR
• Integrated displacement technologies;
• Development of by-passed oil reserves;
• Barrier flooding;
• Non-stationary (cyclical) flooding;

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